Our goal is the development of methods for 1) the specific isolation of antigen-reactive cells for the study of the molecular interactions that occur in their immune reactions, and 2) their application to problems of tumor immunology. In order to be able to directly measure binding of antigen-specific receptors to MHC molecules, we have accomplished the synthesis of conjugates of anti-MHC anti-bodies and water-soluble polymers. In the course of our studies of molecular interactions of antigen-reactive cells as they relate to problems of tumor immunology, we have accomplished improved syntheses of soluble antigen-polymer conjugates ("polygens") and of soluble antibody-polymer conjugates ("poly- bodies"), and have partially characterized these conjugates with respect to size composition, and activity, and have also improved the technique for their synthesis. In studies aimed at understanding the enhanced immunogenicity of a mutagenized ("xenogenized") cell line, we have, with the aid of polyclonal and monoclonal antibodies, partially characterized a cell surface antigen of the xenogenized cell line not found on the original (parental) tumor line.